Scottish explorer Alexander Mackenzie [1764–1820] travelled the river in 1798 the hope it would lead to the Pacific Ocean, but instead reached its mouth on the Arctic Ocean on 14 July 1789. There is a story, likely apocryphal, that he named it “Disappointment River”, but eventually it was named after him.

Mackenzie was also the first European to cross North America north of Mexico. In 1793 the North West Company of Montréal approved Mackenzie’s plan to search for a route to the Pacific Ocean to facilitate the fur trade. Starting in northern Alberta, Mackenzie led a company up the Peace River. They crossed from the Arctic watershed to the Pacific over an unnamed pass that led to the Fraser River, which Mackenzie assumed to be the Columbia River, the Fraser then but little known. South of the big bend in the Fraser, the party headed west over land and reached salt water. Mackenzie concluded that the route was impractical.

“Mackenzie River / Fleuve Mackenzie” is among the 75 “Pan-Canadian names,” large and well-known Canadian features and areas designated in Treasury Board Circular 1983-58 to require presentation in both official languages of Canada on federal maps. In French, a fleuve is a river that flows into an ocean or sea.